External wall insulation is a crucial factor in enhancing building energy efficiency, and its construction must be approached with great care.
Construction Precautions
(1) Ensure the exterior wall’s surface is flat and meets specified standards. All exterior doors and windows should be installed and approved by the relevant authorities.
(2) The gap between door and window frames and the wall must accommodate the thickness of the external insulation layer. These gaps should be tightly filled in layers, and the surfaces of doors and windows must be protected.
(3) Rainwater pipe clamps, embedded metal parts, and wall-through pipes must be installed beforehand, with allowance made for the external insulation thickness.
(4) Construction platforms, such as hanging baskets or dedicated external scaffolding, should be securely erected and pass all safety inspections.
(5) Work should only proceed when the ambient temperature is above 5°C, wind speeds do not exceed level 5 (maximum 10 m/s), and no rain is forecasted. Construction is strictly prohibited during rainy weather.
(6) Except when using integrated decorative cast-in-place concrete exterior wall insulation systems, insulation work should only begin after the base construction has passed quality acceptance.
(7) Size deviations between the plaster layer and decorative layer (especially in thin plaster insulation systems) largely depend on the base surface. Therefore, the base surface dimensions must meet quality standards.
(8) The wall surface must be clean, free of oil stains, dust, and other debris. Loose or weathered material on old walls should be chiseled away, and any protrusions over 10mm should be leveled.
Construction Steps
(1) Surface Cleaning: Remove residual floating ash, release agent oil stains, and any debris from the concrete wall surface. Repair any hollowed plaster areas.
(2) Marking and Layout: Based on facade design and insulation requirements, mark horizontal and vertical control lines, expansion joints, and decorative seams on the wall, especially around doors and windows.
(3) Apply Folded Mesh Cloth: All exposed edges of the polystyrene boards must be covered with folded mesh cloth to reinforce them.
(4) Attach Polystyrene Boards: Standard board sizes are 600mm × 900mm and 600mm × 1200mm. Boards can be cut on-site for irregular areas. Boards larger than 300mm should be placed at wall corners. Avoid placing board joints at the four corners of doors and windows.
(5) Fix Mechanical Anchors: Mechanical anchors should be installed at least 24 hours after applying bonding mortar. Drill holes into the polystyrene boards with an electric hammer, matching hole diameter to anchor size. The drilling depth must meet design specifications. Insert anchors flush with the board surface—nail heads and discs should not protrude.
(6) Surface Polishing: If board joints are uneven, use coarse sandpaper attached to a wooden block to gently polish in circular motions. Remove foam debris with a brush afterward.
(7) Apply Base and Surface Mortar: After the polystyrene boards are secured, apply a polymer mortar base layer. Embed mesh cloth into the mortar, pressing it firmly. Use reinforced mesh at door and window corners, embedding it immediately.
(8) Lay Mesh Cloth: Stretch and press the mesh cloth onto the base mortar layer using a trowel, working from the center outward to ensure it is flat and smooth. Avoid wrinkles and do not press the mesh too deeply. Overlapping mesh should have horizontal overlaps of 100mm and vertical overlaps of 80mm.
Additional Precautions
(1) The surface flatness deviation of polystyrene boards must not exceed 4mm. If it does, polish protrusions and repair concave areas.
(2) When bonding prefabricated boards, even if bonding mortar overflows clearly from the edges, no ash-like debris should appear between the boards.
(3) Board joints must be tightly sealed. If gaps exceed 2mm, fill them with polystyrene strips of matching thickness. Joint height differences should not exceed 1.5mm; otherwise, polish the surface smooth.
(4) Hang vertical reference lines at building corners and other key locations, and horizontal lines on each floor to control the verticality and flatness of the polystyrene boards.
(5) When laying mesh cloth, apply an additional layer of plaster mortar before the base mortar sets, just enough to cover the mesh and slightly reveal its texture.
(6) Avoid continuously kneading the surface mortar to prevent hollow formation.
Article source: Architectural Technology Magazine
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